The present invention relates in general to impedance tomography, and in particular to a new and useful method and apparatus for the simplified generation of current patterns for use in electric current computed tomography (ECCT) which includes synchronization for eliminating transients in switched RC coupled circuits used to practice the invention.
An apparatus for practicing electric current tomography comprising 32 electrodes and a plurality of current generators is disclosed in an article by Newell, Gisser and Isaacson entitled "An Electric Current Tomograph", IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, Vol. 35, No. 10, October 1988.
A process and apparatus for utilizing a similar array of electrodes in computed tomography is disclosed in U.S. Pat. No. 4,920,490 granted to one of the co-inventors of the present application on Apr. 24, 1990. U.S. Pat. No. 4,920,490 and the subject matter therein is assigned to and owned by the assignee and the owner of the invention defined herein at the time the invention defined herein was made. The invention defined herein was made before the date U.S. Pat. No. 4,920,490 was granted.
UK Patent GB 2,138,148 to Smith published Jul. 30, 1986 discloses another apparatus and method of measuring impedances in a zone of the body, which utilizes a large number of electrodes placed in contact with the body, to which currents are applied. Potential differences are then derived which result from the currents through various zones of the body. These potential differences are representative of the impedance of these zones.
Walsh functions are a special set of mathematical functions first described in 1923. One of the special characteristics of a Walsh function is that it only has two values, either -1, or +1. These two values are conveniently converted to the two binary states of zero (0) and one (1). Unlike Fourier analysis which is based on sets of sine and cosine functions, analysis using Walsh functions is based on sets of square waves, which at any point in time, may only have a value of +1 or -1. The characteristics of Walsh functions are well known in the literature and these characteristics are advantageously used in the present invention.